Functional defects in sperm from SPAG16L disrupted mice.
Kathleen A. Lesich1, Zhibing Zhang2, Courtney Biondi1, Kristen L. Ponichter1, Jerome F. Strauss III2, and Charles B. Lindemann1
Sperm from mice homozygous for a disrupted Spag16L gene (KO sperm), which encodes a central apparatus protein, were examined to assess their flagellar motor functions. The beat frequency, bend curvature and shear angle development of live sperm carrying the defect were compared to those of age- and-strain-matched control sperm. Live KO sperm exhibited much less bending of the flagellum during the beat. Shear angle analysis showed that the amount of microtubule sliding in the R-bend direction of the beat was selectively restricted. This suggests that there is limited activation of the dyneins on one side of the axoneme in the live cells. The KO sperm were also demembranated with Triton X-100 and examined for their response to free Ca2+ and for their ability to undergo microtubule sliding driven by dynein action. The flagellar curvature response to Ca2+ is significantly (p < 0.001) reduced in the KO sperm. The Ca2+ response requires the activation of the dyneins on outer doublets 1, 2, 3 and 4. These are the same dyneins required for R-bend formation. In axonemes prepared to disintegrate by microtubule sliding, we observed little or no extrusion of doublets 1 and 2, which is consistent with a reduced activity of their dyneins. In addition, the passive flagella inhibited by sodium metavanadate to disable the dyneins were examined for mechanical abnormalities. We discovered that the midpiece region of the KO sperm is more rigid than that of wild-type sperm. The deficit we observed in motor function, together with the increased rigidity of the midpiece region can account for the motility characteristics of the SPAG16L disrupted sperm. The lack of a normal response to Ca2+ would render these sperm incapable of hyperactivation, which might explain the infertility associated with this defect. Our findings implicate an important role for the central apparatus in Ca2+ induced hyperactivation.
Supported by N.S.F. grant MCB-0516181 (CBL) and N.I.H. grant HD037416 (JFS).